Oscar I - no water heating

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by shoki222 » Aug 14, 2019, 12:23 am


When I switched on the oscar 1 machine, the heating element lamp is dark. the water in the boiler does not getting heated.
upon checking, the boiler heating element has ~50 ohm and 220 volts are present at the in and out electrode (each, relative to ground) and also the thermostat element is in 0 ohm. between the 2 heater electrodes the voltage is 0.

I think that the reason that the water does not heated is that there is no voltage across the electrode. the machine has to drop one of the electrodes to ground in order to create voltage fall across the heater.

pressurestat is good, and I also tried to short him.

please advise.

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#2: Post by Jake_G » Aug 14, 2019, 12:44 am


Did you disconnect the heating element before testing? 50 ohms should get you just shy of 1,000W of heating, which seems a little low, but within reason. If the wires were connected, you would have been measuring the total resistance of the circuit and you would have no idea if you had an open circuit at the element.


- Jake


#3: Post by shoki222 » Aug 14, 2019, 12:47 am

yes, i disconnect the wires from the boiler electrodes. ~50 ohm is the specifications it is good.

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#4: Post by Jake_G » Aug 14, 2019, 1:15 am

Peculiar indeed.

Voltage and ohms gives you heat. There is very little way around that. How are the terminals? Signs of corrosion or oxidation?

It is worth taking a wire brush to the terminals and also looking at the crimps on the wires. How are you measuring voltage at the element? Are you reading 220V on the poles of the element itself, or at the wires leading to it?


- Jake


Just saw that you measured each electrode relative to ground. You have a closed open neutral in the circuit, hence the dim lamp. I am not familiar enough with Oscar to give you specific helpful insight, but trace your neutral back from the power switch and you'll find an open circuit.

Does the pressurestat switch the hot and the neutral or just one?

Edit #2
I found this schematic over on CG:
Image: Oscar Schematic originally posted here

Looks to me like you have either a stuck open pressurestat or safety thermostat. Not sure if the safety thermostat can be reset or not. It's worth looking into why it might have tripped if that's the problem.

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#5: Post by plindy » Aug 14, 2019, 5:05 am


I concur with Jake_G, early Oscar's have a resettable hi-limit switch on the boiler just above the heating element. To reset push the red button in the middle. Later Oscars have a non-resettable thermal fuse in the heating element. Which I believe can be replaced.
The no water light not lit, is a good sign as the brain box will cut power to the element when low water is detected.


#6: Post by shoki222 » Aug 14, 2019, 5:31 am

actually I found out that the no water light is always off even when the outside water tank is empty and the pump suck out all the water remains. the retaining valve, the element below the water tank change his transitivity as function of the water absence\existence.
do you think it is the brain box?

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#7: Post by plindy » Aug 15, 2019, 5:24 am

So is this machine a reservoir, Direct connect, or non pressurized outboard tank?

On the reservoir machine, the fixture below the reservoir needs to be filled 3/4 full. Even then it may take a few seat/unseat/reseat cycles to establish flow.
A direct connect machine will have the site water pressure to feed the pump.
A non pressurized plumbed machine can pull water from an outboard source.
However a direct connect and non pressurized machine will have the brain bypassed by connecting the two green/yellow sensor wires.
All versions must have water at the pump, for the pump to work. [sorry a bit obvious]

With water at the pump, you can engage the brew button, then engage the on/off button.
Sometimes this helps kickstart the water delivery.

Any water events around the brain?


#8: Post by shoki222 » Aug 15, 2019, 7:20 am

no water event around brain box.
I have white plastic water tank inside the oscar body.

when I put out the water tank' and suck all the water remains from the sensor, this by operating the pump, even when there no water at all' the pump do not stop and there is no "no water" lite on.

how to test the sensor that located under the water tank?

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#9: Post by plindy » Aug 15, 2019, 12:53 pm

The sensor is a male tab connecter, plus the female connecter on the sensor wire. A sheer metal screw holds the tab to the fixture under the reservoir. The screw goes all the way thru the fixture, and the water completes the circuit. Check all of these components for conductivity.

Or the start/stop switch, and or wiring to may be suspect.